1. Field of the Invention
This invention lies in the field of electroporation, i.e., the process by which exogenous molecular species are inserted into membranous structures by suspending the structures in a liquid solution of the exogenous species and applying an electric field to the suspension. In particular, this invention addresses the apparatus for performing electroporation in a multitude of cell suspensions either simultaneously or in rapid succession.
2. Description of the Prior Art
Electroporation, or electric pulse-driven transfection, is widely used for impregnating membranous structures, such as living biological cells, liposomes, and vesicles, with exogenous molecules. The liquid in which the structures is suspended is typically an aqueous solution of the exogenous species in a high-conductivity buffer. Normal saline is commonly used as the buffer since, in addition to offering relatively low resistance to an electric current, normal saline provides an environment that is favorable to the viability of most membranous structures. The transfection of multiple samples of membranous structure suspensions either simultaneously or in rapid succession by electroporation is known as “high-throughput electroporation,” a procedure that is useful in siRNA experiments, in research using cDNA libraries, and in numerous other manipulations of membranous structures that are practiced in biotechnology laboratories. In high-throughput electroporation, the samples undergo transfection in the wells of a multi-well plate that contains electrodes embedded in each well. Typical multi-well plates have the standard 96-well configuration of microplates, which serves the user well in many applications but offers only limited options when there is a need to transfect samples that are larger than the volumes of individual wells or samples that are smaller in number than the standard 96.
Plates for high-throughput electroporation also require a certain degree of precision in manufacturing, since uniform well size and electrode area and the absence of cross contamination between wells are important for controlled, reliable, and uniform transfection. The usually efficient and economical process of injection molding is conveniently used in electroporation plate manufacture but is complicated due to the need to form the plastic walls around the metal electrodes. Improperly formed plates are prone to wicking, for example, which occurs in a number of ways. One of these arises from the fact that the electrodes in the wells are often designed to leave a gap between the vertical edge of the electrode and the end wall of the well. The hot plastic used in the molding tends to draw away from the relatively cool electrode, and this drawing away can leave a narrow channel through or along an otherwise solid wall separating the wells. Capillary action through this channel can result in cross contamination between wells. Another wicking problem can arise when an electrode is not securely held against the wall of the well during the molding process. A small gap between the electrode and the wall can cause liquid from the cell suspension to be drawn up into the gap by capillary action, and possibly into an adjacent well. Improperly formed plates can also arise when hot plastic leaks into areas that are intended to be left open to form the wells. A single well that is defective for any of these reasons can require that an entire plate be discarded.
These and other limitations and sources of inefficiency in well plate design and manufacture are addressed by the present invention.